Solid state electronic devices can be fabricated with conjugated organic polymer layers. Conjugated polymer-based diodes and particularly light emitting diodes (LEDs) and light-detecting diodes are especially attractive due to their potential for use in display and sensor technology. This class of devices has a structure that includes a layer or film of an electrophotoactive conjugated organic polymer bounded on opposite sides by electrodes (anode and cathode) and carried on a solid substrate.
Generally, materials for use as active layers in polymer diodes and particularly PLEDs include semiconducting conjugated polymers that exhibit photoluminescence. In certain preferred settings, the polymers exhibit photoluminescence and are soluble and processible from solution into uniform thin films.
The anodes of these organic polymer-based electronic devices are conventionally constructed of a relatively high work function metal. This anode serves to inject holes into the otherwise filled p-band of the semiconducting, luminescent polymer.
Relatively low work function metals, such as barium or calcium, are preferred as the cathode material in many structures. This low work function cathode serves to inject electrons into the otherwise empty p*-band of the semiconducting, luminescent polymer. The holes injected at the anode and the electrons injected at the cathode recombine radiatively within the active layer and light is emitted.
LED lighting can commonly be characterized by on-axis luminous intensity expressed in candela. Intensity describes the flux per solid angle radiated from a source of finite area. Furthermore, flux is the total amount of light emitted from a source in all directions. For the purpose of this invention, flux will be used to describe the brightness of LEDs.
Radiometric light is specified according to its radiant energy and power without regard for the visual effects of the radiation. Photometric light is specified in terms of human visible response according to the CIE standard observer response curve. Furthermore, in the fields of photonics and solid state physics, luminous efficacy is defined as the conversion between photometric flux, expressed in lumens, and radiometric flux, expressed in watts.
It is noted that the luminous efficacy is a function of the dominant wavelength of a specific LED lighting source. For example, an Indium Gallium Nitride (InGaN) LED shows increasing luminous efficacy from 85 to 600 lumens per watt corresponding to a shifting of the dominant wavelength from 470 to 560 nm. On the other hand, an Aluminum Indium Gallium Phosphide (AlInGaP) shows decreasing luminous efficacy from 580 to 800 lumens per watt corresponding to a shifting of the dominant wavelength from 580 to 640 nm. For the purpose of this invention, luminous efficacy at the peak transmittance of LED is referred.
Most typical prior art LEDs are designed to operate no more than 30-60 milliwatts of electrical power. More recently, commercial LEDs capable of continuous use at one watt of input power were introduced. These LEDs use much larger semiconductor chips than previous LEDs to handle the large power. In order to dissipate heat to minimize junction temperature and maintain lighting performance, these larger chips are normally mounted to a more effective thermal conductor (such as metal slugs) than previous LED structures.
Typically, the 5-watt LEDs are available with efficacy of 18-22 lumens per watt; the 10-watt LEDs are available with efficacy of 60 lumens per watt. These 10-watt LED light devices will produce about as much light as a common 50-watt incandescent bulb and will facilitate use of LEDs for general illumination needs.
Despite the LED devices currently available, a need still exists for improved LED modules which can provide improved performance characteristics, such as increased heat dissipation qualities, improved manufacturing processes, and lower cost benefits. Other benefits include closer TCE match to the chip, smaller size, light weight, environmental stability, increased circuit integration capability, enhanced light reflectivity, simplified fabrication, higher yield, broader process tolerance, high mechanical strength, and effective heat dissipation. None of the prior art LEDs provide for the use of a thick film dielectric paste composition in the formation of a LED chip carrier and LED module which leads to improved dielectric properties in the base material (anodized layer in some embodiments) and therefore improved performance characteristics.
Existing technology or materials may not be able to withstand high heat applications, especially during processing. Typical organic materials are cured at less than 300° C. Thick film technology can withstand high heat applications such as those applications above 300° C.
One example is U.S. Pat. No. 5,687,062 to Larson. Larson discloses a thermally efficient circuit board which has a base layer with high thermal conductivity and a thermal expansion coefficient close to that of silicon, such as aluminum carbide. Above the base layer is a layer of anodized metal, either a separate material, such as aluminum, which is formed on the base and then anodized, or an anodized portion of the base itself. To the anodized metal is then applied a sealant material of lower thermal conductivity, but good electrically insulative and adhesive qualities, such as Teflon® FEP. The sealant flows into cavities in the porous anodized metal structure, creating a well-anchored bond. A metal foil layer is then bonded to the surface of the sealant, and used to pattern conductive circuit paths using conventional methods. Larson discloses that the microscopic cavities of the anodized metal allows anchoring of the sealant material which flows into its pores. Larson further discloses that the Teflon® FEP is heated to its melting temperature of 300° C., and is then forced at a pressure of 275 psi into the porous surface of the aluminum oxide where the anodized metal functions as a matrix for the sealant resulting in an anchoring of the sealant to the anodized metal.
For example, printed circuit board designs are typically formed with such organic materials and cannot withstand the high temperatures necessary for high heat applications. The present invention is useful in high temperature, high heat applications, like high power LED applications.
Various design and configuration of the LED chip carrier devices have been provided in the art. However, they all presented problems related to various functions, manufacturability, and cost. Functioning LED devices with superior performance characteristics are still needed for lighting applications, including modules for LCD applications, which allow for the improvement in heat dissipation properties and thermal conductivity properties to improve the overall color quality of emitting light diode modules and increase the module life. Furthermore, there still exists a need for a LED device which allows for a decrease in production costs and the ability to produce a LED device with a large area. The present inventors have provided such materials, methods, chip carriers, and modules to allow for such an innovation in lighting technology.